The basic rule is: the further you turn away from the wind, the further you let the sails out, and as you turn towards the wind you pull them in. Then fine-tune by easing each sail until its luff just starts to flutter and pulling it back in a little.
Trimming means adjusting the sails to suit the wind. It starts with one rule: turn away from the wind and let the sails out; turn towards it and pull them in.
- Close-hauled, as close to the wind as the boat will sail, the sails are pulled in tight.
- On a beam reach, with the wind across the side, they are about halfway out.
- On a broad reach and a run, they are well out, the mainsail as far as the shrouds allow.
That gets you close. To get it exactly right, use the sail itself:
- Ease the sheet slowly until the luff of the sail just starts to flutter or curl.
- Pull it back in until the flutter stops, and a little more.
- On the jib, check the telltales: both should stream back. Windward one lifting, pull in; leeward one drooping, ease out.
- On the mainsail, watch the leech telltales. They should stream aft most of the time; if they keep disappearing behind the sail, ease the mainsheet.
Trim the jib first, then the mainsail to match it. The wind is always changing a little in strength and direction, and each time you alter course the sails need adjusting, so the sheets are never set and forgotten.
The commonest mistake is sails pulled in too tight. They look full and the boat heels more, but the air has stalled on the leeward side and she is slower. When in doubt, let it out until it luffs, then bring it back.
Trim also affects how the boat steers. A mainsail pulled in too hard makes the boat pull towards the wind, with heavy weather helm. Easing the mainsheet or moving the traveller to leeward will make her lighter on the helm and faster.
More in the book: Chapter 5, Trimming the sails